Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Dead Man's Snitch - Monitor Cron Jobs and Windows Scheduled Tasks with ease.
Simple Ops - Simplify website performance and uptime monitoring with alerting, ssl check, chrome ux metrics, multi locations
Cronhub - Cronhub helps you to easily monitor all your cron jobs in a beautiful dashboard. It alerts you when your cron job doesn't run on time or it fails.
UptimeRobot - Free Website Uptime Monitoring